The present invention relates to a method of establishing a clock in the I/O card of a personal computer and more particularly to a method of establishing a control clock in the UART of the I/O card of a personal computer.
Conventional I/O cards of a personal computer usually include a device for receiving data bits from the central processing unit and transmitting the same to the desired peripheral equipment. This circuit element, included in a standard I/O card, was first developed by Intel Inc. and is referred to as the Universal Asynchronized Receiver and Transmitter, commercially abbreviated as UART. A traditional I/O card of this type is schematically shown in FIG. 1 . The I/O card 10 includes a UART circuit 11 which is operated at a frequency of 1.8432 MHz. This I/O card 10 is used with a PC/AT having a connection slot which provides a clock from the main board to the I/O card through the connectors 13 thereon. The clock of the main board operates at a frequency of 14.31818 MHz.
A conventional and typical combined graphic and I/O card is schematically shown in FIG. 2. The card 20 includes all the circuit elements of a standard I/O card represented by block 21 and operates according to a clock generated by the crystal 22 at a frequency of 1.8432 MHz. Another graphic data processing circuit 23 is also included in the card 20 and operated according to another clock generated by a second crystal 24 at a frequency of 16 MHz.
From the above described conventional I/O cards used in a PC/AT, an independent crystal has been used to generate a control clock for the UART circuit on the I/O card. For the purpose of reduction of the manufacturing cost of an interface I/O card and to same pin count, the crystals for the UART circuit can possibly be eliminated.